Stroke results in significant moribidity and mortality. The only proven therapy for acute stroke is the thrombolytic agent, rt-PA, which must be given within three hours of symptom onset. GV150526 is a potent glycine antagonist which has shown promise in reducing brain damage in laboratory acute stroke models. It has also proven safe and tolerable in phase 1 and phase 2 trials in the dose to be used in this study. The primary objectives of this Phase 3 clinical trial are (1) to demonstrate the efficacy of GV150526 by showing an improvement in functional outcome (independence) at month 3 between treatment groups in patients with ischemic (non-hemorrhage) stroke in patients receiving medication up to 6 hours symptom onset; and (2) to demonstrate further the safety of GV950526 in the clinical setting of acute stroke. Secondary objectives include assessment of the safety and preliminary efficacy of GV150526 in patients with intracerebral hemorrhages, examining the relationship between GV150526 and Barthel Index at month 3, examining the relationship between GV150526 and survival, and to measure the effect of GV150526 on medical resource utilization. This is a multicenter, randomized, double-blind, placebo-controlled, parallel group study of a single dosing regimen of GV150526 in patients with acute stroke presenting within 6 hours of symptom onset. Approximately 1600 total patients will be randomized to either GV150526 or placebo in a 1:1 ratio. Assessments of safety, neurological function and disability, and medical resource utilization will be performed during the screen, treatment, and follow-up segments.